Relationship in a number of different species of DNA/cell, nuclear volume, and actual chromosome volume to each other, and of these estimators of genome size to radiosensitivity. Capillary damage by radiation. Comparison of capillary damage to small intestine and kidney, from acute and fractionated radiation, by microangiography. Ozone as a mutagen. Effect of inspired ozone in causing in vivo chromosome aberrations in circulating leukocytes, and lung tumors.